Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.80   10.301%   $272.2229   $272.22   $272.20   $272.20  
  Purchase #2 $244.64   7.331%   $262.5746   $262.57   $262.55   $262.60  
  Purchase #3 $35.80   5.393%   $37.7307   $37.73   $37.75   $37.70  
  Purchase #4 $186.44   9.191%   $203.5757   $203.58   $203.60   $203.60  
  Purchase #5 $110.41   9.444%   $120.8371   $120.84   $120.85   $120.80  
  Purchase #6 $194.92   10.435%   $215.2599   $215.26   $215.25   $215.30  
  Purchase #7 $169.75   8.484%   $184.1516   $184.15   $184.15   $184.20  
  7 purchase totals = $1,188.76       $1,296.3525   $1,296.35   $1,296.35   $1,296.40